1. Field of the Invention
The present invention relates to a method and apparatus for the adjustment of valve lash in motor vehicles having adjustable valve lifter configurations. It is particularly applicable to engines manufactured by the Chevrolet Division of General Motors Corporation.
2. Background Information
Conventional automobile engines have use lifters which typically are interposed between a cam shaft and a push rod to move the push rod up and down as the cam shaft rotates. The push rods in turn engage a rocker arm which pivots up and down in response to movement of the push rod and activates an intake or exhaust valve in the engine. In certain engines, particularly those manufactured by the Chevrolet Division of General Motors Corporation, the individual rocker arms are adjustable to eliminate any slack between the valve stem, rocker arm, push rod and lifter when the valve is in a closed position and the cam is in its lowest position relative to the lifter.
The valve adjusting sequence for a multiple cylinder engine is to start with the engine in what is called the top dead center firing position for the number one cylinder. This position has both the intake and the exhaust valves closed for the number one cylinder. Depending upon whether the engine is a four cylinder, in-line six cylinder, V-6, or V-8, certain of the remaining cylinders will also have either an intake or exhaust valve in a closed position for adjustment purposes. After adjustment of certain designated intake and/or exhaust valves, the engine is typically rotated one full revolution in the normal direction of rotation to place all the remaining unadjusted valves in closed positions at which time they may be adjusted.
Adjustment of rocker arm nuts in an engine is typically necessary whenever any work is performed which affects the valve train. The specific adjusting sequence for any particular engine is generally described in the Service Manuals and will inform the mechanic as to which specific valves should be adjusted in the first or top dead center fire position for number one cylinder, and the remaining sequence for the other valves after rotation of the engine one full turn. A disadvantage of the present method of performing these adjustments is that the mechanic is forced to constantly refer to the service manual to determine the proper valve to be adjusted on a particular cylinder at a given position of the engine relative to the number one cylinder. This is time consuming, inefficient and can lead to errors in the adjusting sequence if a particular valve is forgotten or adjusted out of sequence.